This invention relates to safety devices, and more particularly, to safety devices for self-propelled machines used for compacting earth, asphalt and the like, operated by a driver using a steering rod connected to the machine and walking behind the machine. The safety device is intended to stop the forward or reverse movement of the machine by cutting off the hydraulic fluid to the machine's drive system when the driver releases his grip on the operating handle of the steering rod.
Safety requirements related to the operation of self-propelled machines of various types have increased according to the increase in the use of such machines. This is particularly true of machines of the type known as pedestrian control machines, i.e., machines designed so that the driver does not sit on the machine but walks beside or behind it. If the driver should stumble or lose his grip on the operating handle, there is a considerable risk that the self-propelled machine will continue its progress uncontrolled and seriously injure the driver or other persons nearby or damage the surroundings.
One example of a machine of a type for which the invention is primarily intended is a self-propelled, hydraulically powered, vibrating roller for packing earth, asphalt or the like that is operated with the aid of a steering rod mounted on the rear section of the roller. If the roller is reversed, and the driver stumbles and loses his grip on the operating handle, the roller will continue its reverse movement and may, if it is not equipped with any safety device, cause serious injury to the driver.
Processing machines of this type, which are operated via a steering rod connected to the machine, have been known to be equipped with what is commonly termed a dead man's grip on the operating handle of the steering rod. The dead man's grip consists of a handle which the driver keeps depressed against the operating handle, thus counteracting the pressure from, for example, a spring, as long as the machine is being used.
The dead man's grip, however, becomes tiring for the operator in the long run. In order to avoid such discomfort, proposals have been made, as, for example, in accordance with Swedish Pat. No. 380,569, which use a spring loaded bar in which a spring prevents the bar from assuming a break position so long as the machine is being used and as long as the driver grips the operating handle with his hands. This safety bar will, however, press against the forearms or wrists of the driver all the time. Since the safety bar will strike the driver's arms with a force corresponding to the spring force, the driver's arms will gradually become fatigued. This discomfort is particularly accentuated in the case of vibrating machines.